Heat transfer surfaces are the surfaces through which heat energy passes from one object or fluid to another. The prime heat transfer surface of heat exchangers, such as an air-to-air heat exchanger, transfers the heat energy from a hot fluid to a cool fluid both of which are flowing through the heat exchanger. Also, because mixing of hot and cool fluids is not generally permitted, the transfer surface also functions as the pressure boundary between the fluids. One way of dissipating heat energy from a hot object to a cooling medium is by affixing a number of fin like structures directly to the object or to a heat sink affixed to the object; the fins transfer the heat energy to the cooling medium.
A simple heat transfer surface is a smooth, flat surface. Such a surface, however, does not transfer heat energy as readily as do other non-planar surfaces, such as plates with protruding pins, wavy-fin plates and louvred plates. The best of these is the plate with protruding pins. However, the manufacturing of these plates is difficult, time consuming and expensive.
These protruding pin heat transfer surfaces have been made in accordance with the methods disclosed in U.S. Pat. Nos. 3,327,779 and 3,399,444. These methods, however, involve a number of manufacturing steps, typically including fixing a plurality of U-shaped wires to the surface of the hot object or a plate affixed to the object. These heat transfer surfaces have been also been made by casting, or by sawing away the metal block material to create the projections. In the machining method the pins are not optimal for heat transfer because of their square or hexagonal cross-sectional shape.
Protruding pin heat transfer surfaces have been used in compressor aftercoolers and/or intercoolers, where the cooling fluid was water, and in hydraulic system heat exchangers where the cooling fluid was air or water. In these applications solid pins were affixed to the surface of a pipe or tube being used as the prime heat transfer surface and pressure boundary.
Since these transfer surfaces are difficult, time consuming and expensive to manufacture, they have been generally used only when optimization of heat transfer is more important than cost considerations. In other situations, were space limitations do not require optimization of heat transfer, less expensive heat transfer surfaces are typically used.